Heat recovery system

ABSTRACT

A heat recovery system includes a plurality of heat source portions; a heat exchanger connected to the heat source portions via a primary flow path portion through which a first fluid flows, and configured to perform heat exchange between the first fluid and a second fluid; a valve mechanism configured to select a flow path that connects the heat exchanger and the heat source portions; and a power generation unit connected to the heat exchanger via a secondary flow path portion through which the second fluid flows, and configured to generate electric power using the second fluid. Timing of a temperature rise of the first fluid in one heat source portion is different from that in another heat source portion. The valve mechanism operates in accordance with the timing of the temperature rise of the first fluid in each of the heat source portions.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2018-198619 filed on Oct. 22, 2018 and Japanese Patent Application No. 2018-235453 filed on Dec. 17, 2018, each including the specification, drawings and abstract, is incorporated herein by reference in its entirety.

BACKGROUND 1. Technical Field

The disclosure relates to a heat recovery system.

2. Description of Related Art

There is known binary electric power generation in which hot water or vapor is used as a heat source to heat and vaporize a heating medium with a low boiling point to generate electric power. The binary electric power generation can effectively utilize waste heat at a relatively low temperature, and is employed for geothermal electric power generation etc., for example.

In recent years, there has been an attempt to use waste heat output from a factory or a facility, for example, for the binary electric power generation (see Japanese Patent Application Publication No. 2017-129059, for example).

SUMMARY

FIG. 8 illustrates a facility in which a binary power generation unit 91 (hereinafter referred to as a “power generation unit 91”) is employed in conjunction with a heat treatment device 90 that performs heat treatment (hardening treatment, i.e., quenching treatment) of a metal part. This facility includes an oil tank 92 of the heat treatment device 90, the power generation unit 91, and a heat exchanger 93. The oil tank 92 stores a cooling liquid 99. The oil tank 92 and the heat exchanger 93 are connected to each other through a primary pipe 94. The heat exchanger 93 and the power generation unit 91 are connected to each other through a secondary pipe 95. Heat treatment (hardening treatment, i.e., quenching treatment) is performed by immersing an object 100, which has been heated, in the cooling liquid 99 in the oil tank 92 such that the object 100 is cooled. This heat treatment temporarily raises the temperature of the cooling liquid 99. When the cooling liquid 99 flows through the primary pipe 94, heat (waste heat) of the flowing cooling liquid 99 is transferred (heat exchange is performed), in the heat exchanger 93, to a heating medium 98 that flows through the secondary pipe 95. The power generation unit 91 generates electric power using the heat of the heating medium 98, and the cooling liquid 99 is cooled.

In this manner, the power generation unit 91 generates electric power using the cooling liquid 99, the temperature of which has been raised, as a heat source. In order to generate electric power, however, it is necessary that the temperature of the cooling liquid 99 should be a predetermined temperature or higher.

In the heat treatment device 90 described above, the time interval (a cycle time T in FIG. 9) in which the object 100 is immersed in the oil tank 92 is long (e.g. 30 minutes), and the time interval (cycle time T) is varied in accordance with conditions such as the weight of the object 100. When the object 100 which has been heated is immersed in the oil tank 92, the temperature of the cooling liquid 99 is raised. Electric power can be generated for a predetermined time (Δt in FIG. 9), when the temperature of the cooling liquid 99 is higher than the predetermined temperature A. When the temperature of the cooling liquid 99 is dropped to the predetermined temperature A, however, electric power cannot be generated.

In the case where the heat of the cooling liquid 99 in the heat treatment device 90 is utilized for electric power generation, the temperature of the cooling liquid 99 is varied in accordance with treatment conditions such as the heating temperature, weight, etc. of the object 100, and also varied in accordance with the lapse of the time. If such variations are irregular, electric power generation performed by the power generation unit 91 is unstable, and there is a possibility that the power generation unit 91 does not function in many time periods. Such problems may occur not only in the case where the power generation unit 91 is employed in conjunction with the heat treatment device 90 described above, but also in the case where the power generation unit 91 is employed in other facilities.

FIG. 15 illustrates a facility in which a binary power generation unit 191 (hereinafter referred to as a “power generation unit 191”) is employed in conjunction with a heat treatment device 190 that performs heat treatment (hardening treatment, i.e., quenching treatment) of a metal part. In this facility, an oil tank 192 of the heat treatment device 190 and the power generation unit 191 are connected to each other through a pipe. The oil tank 192 stores a cooling liquid 199 that cools an object which has been heated. The power generation unit 191 includes a heat exchanger (vaporizer) 193, a power generation device 195 that includes an expansion unit 194, a condenser 196, etc. The oil tank 192 and the heat exchanger 193 are connected to each other through a pipe 197 on the primary side. The heat exchanger 193 and the expansion unit 194 are connected to each other through a pipe 198 on the secondary side.

Heat treatment (hardening treatment, i.e., quenching treatment) is performed by immersing the object, which has been heated by the heat treatment device 190, in the cooling liquid 199 in the oil tank 192 such that the object is cooled. This heat treatment raises the temperature of the cooling liquid 199. The cooling liquid 199, the temperature of which has been raised, flows through the pipe 197 on the primary side, and the heat of the cooling liquid 199 is transferred (heat exchange is performed) to a heating medium 200 on the secondary side in the heat exchanger 193. The heating medium 200, which has been gasified through the heat exchange, is input to the expansion unit 194 through the pipe 198 on the secondary side to generate electric power. The heating medium 200, which has passed through the expansion unit 194, flows to the condenser 196 to be liquefied, and returns to the heat exchanger 193.

While the cooling liquid 199 is fed from the oil tank 192 to the heat exchanger 193 through the pipe 197 on the primary side, heat of the cooling liquid 199, the temperature of which has been raised, is released to the atmosphere. In order to restrain the heat release, the pipe 197 on the primary side is covered by a heat insulating material. The outside temperature around the pipe 197 on the primary side is about 20° C. (a normal temperature, i.e., an ordinary temperature), while the temperature of the cooling liquid 199 which flows through the pipe 197 on the primary side is about 120 to 130° C., for example, and there is a large temperature difference therebetween. Therefore, the temperature of the cooling liquid 199 is dropped while the cooling liquid 199 flows through the pipe 197 on the primary side, even if the heat insulating material is provided. That is, thermal energy of the cooling liquid 199 is decreased through the heat release from the pipe 197 on the primary side.

The temperature of the cooling liquid (first fluid) 199 which flows through the pipe 197 on the primary side significantly affects the power generation efficiency of the power generation device 195.

The disclosure provides a heat recovery system in which electric power generation can be efficiently performed even in the case where the temperature of waste heat obtained from a heat source portion is varied, for example. The disclosure also provides a heat recovery system that can enhance the power generation efficiency by restraining a temperature drop of a first fluid.

A first aspect of the disclosure relates to a heat recovery system including a plurality of heat source portions configured to raise a temperature of a first fluid using heat obtained by treating an object; a heat exchanger connected to the plurality of heat source portions via a primary flow path portion through which the first fluid flows, and configured to perform heat exchange between the first fluid and a second fluid; a valve mechanism provided in the primary flow path portion and configured to select a flow path that connects the heat exchanger and the heat source portions; and a power generation unit connected to the heat exchanger via a secondary flow path portion through which the second fluid flows, and configured to generate electric power using the second fluid as an input. Timing of a temperature rise of the first fluid in one of the heat source portions is different from timing of a temperature rise of the first fluid in another of the heat source portions, and the valve mechanism operates in accordance with the timing of the temperature rise of the first fluid in each of the plurality of heat source portions.

In the heat recovery system according to the above aspect, the plurality of heat source portions share the power generation unit. The timing of the temperature rise of the first fluid in the one heat source portion is different from the timing of the temperature rise of the first fluid in the other heat source portion. Therefore, when the first fluid, the temperature of which has been raised by the one heat source portion, is supplied to the heat exchanger, heat exchange is performed (i.e., heat is transferred) between the first fluid and the second fluid, and the power generation unit generates electric power using the second fluid as an input. After that, even in the case where the temperature of the one heat source portion is decreased and it becomes impossible to generate electric power, the first fluid, the temperature of which has been raised by the other heat source portion, is supplied to the heat exchanger. Herewith, heat exchange is performed (i.e., heat is transferred) between the first fluid and the second fluid, and the power generation unit can generate electric power using the second fluid as an input. Thus, the power generation unit is given more opportunities to operate by differentiating respective timings of the temperature rise of the first fluids between the plurality of heat source portions. Thus, electric power generation can be efficiently performed by the power generation unit. Note that, the timing to start the cycle of the heat source portion (heat treatment device) can be intentionally shifted at the heat source portions side (heat treatment devices side)

The primary flow path portion may include a main flow path that connects the heat source portions and the heat exchanger, and a coupling flow path that connects the heat source portions to each other to enable movement of the first fluid between the heat source portions; and the valve mechanism may include a valve configured to switch the flow path such that, in a case where the temperature of the first fluid in the one heat source portion is raised, the first fluid flows to the other heat source portion through the coupling flow path and the first fluid flows to the heat exchanger by way of the other heat source portion. In this configuration, the flow path is switched such that, in the case where the temperature of the first fluid in the one heat source portion is raised, the first fluid flows to the other heat source portion through the coupling flow path and the first fluid flows to the heat exchanger by way of the other heat source portion. On the other hand, the flow path is switched such that, in the case where the temperature of the first fluid in the other heat source portion is raised, the first fluid flows to the one heat source portion through the coupling flow path and the first fluid flows to the heat exchanger by way of the one heat source portion. When the heat source portions are connected to each other through the coupling flow path as in the above configuration, the heat source portions can be regarded as a single heat source portion, and the volume of the first fluid that serves as a heat source is increased. Therefore, the temperature rise of the first fluid due to heat obtained by treating the object is mitigated, but the temperature of the first fluid that has been raised is not easily lowered. Thus, the time (i.e., the time period) for which the power generation unit can generate electric power can be elongated as compared to the related art. Further, as described above, the power generation unit is given more opportunities to operate by differentiating respective timings of the temperature rise of the first fluids between the plurality of heat source portions. Thus, electric power generation can be further efficiently performed by the power generation unit.

A second aspect of the disclosure relates to A heat recovery system including a plurality of heat source portions configured to raise a temperature of a first fluid using heat obtained by treating an object; a heat exchanger connected to the plurality of heat source portions via a primary flow path portion through which the first fluid flows, and configured to perform heat exchange between the first fluid and a second fluid; a valve mechanism provided in the primary flow path portion and configured to select a flow path that connects the heat exchanger and the heat source portions; and a power generation unit connected to the heat exchanger via a secondary flow path portion through which the second fluid flows, and configured to generate electric power using the second fluid as an input. The primary flow path portion includes a main flow path that connects the heat source portions and the heat exchanger, and a coupling flow path that connects the heat source portions to each other to enable movement of the first fluid between the heat source portions. The valve mechanism includes a valve configured to switch the flow path such that, in a case where the temperature of the first fluid in one of the heat source portions is raised, the first fluid flows to another of the heat source portions through the coupling flow path and the first fluid flows to the heat exchanger by way of the other heat source portion.

With the heat recovery system according to the above aspect, since the heat source portions are connected to each other through the coupling flow path, the heat source portions can be regarded as a single heat source portion, and the volume of the first fluid that serves as a heat source is increased. Therefore, the temperature rise of the first fluid due to heat obtained by treating the object is mitigated, but the temperature of the first fluid that has been raised is not easily lowered. Therefore, the time (i.e., the time period) for which the power generation unit can generate electric power can be elongated as compared to the related art. Thus, electric power generation can be efficiently performed by the power generation unit.

The power generation unit may be a binary power generation unit. In this case, waste heat at a relatively low temperature can be utilized effectively.

According to the above aspects of the disclosure, it is possible to efficiently perform electric power generation even in the case where the temperature of waste heat obtained from the heat source portions is varied, for example.

A third aspect of the disclosure relates to a heat recovery system including a primary-side flow path through which a first fluid flows from a heat source; a heat exchanger configured to perform heat exchange between the first fluid, which flows through the primary-side flow path, and a second fluid; a secondary-side flow path through which the second fluid flows; a power generation device configured to generate electric power using the second fluid in the secondary-side flow path; and a condenser configured to cool and condense the second fluid that has passed through the power generation device. The primary-side flow path includes a multi-walled pipe that includes an inner flow path portion through which the first fluid passes and an outer flow path portion provided around the inner flow path portion. The outer flow path portion is supplied with heated air obtained through heat output from a waste heat output portion that is at least one of the heat source, another heat source, and the condenser.

With the heat recovery system according to the above aspect, the energy that has been discarded as waste heat in the related art can be utilized again. That is, the temperature decrease of the first fluid that flows through the inner flow path portion of the multi-walled pipe can be restrained by supplying the heated air that is obtained through heat output from the waste heat output portion to the outer flow path portion of the multi-walled pipe. As a result, it is possible to enhance the efficiency of electric power generation performed using the second fluid.

The primary-side flow path may include a first pipe that allows the first fluid to flow from the heat source to the heat exchanger; the first pipe may include the multi-walled pipe; and the heat recovery system may include a connection pipe through which the heated air is supplied from the waste heat output portion to the outer flow path portion of the multi-walled pipe. With this configuration, the temperature decrease of the first fluid that flows to the heat exchanger through the first pipe can be restrained effectively.

The multi-walled pipe may include a main pipe and a sub pipe; a heat insulating material may be provided at an outer periphery of the main pipe, and an inside of the main pipe may serve as the inner flow path portion; and the sub pipe may be provided around an outer peripheral side of the main pipe such that a flow path with an annular cross section that serves as the outer flow path portion is configured. In this configuration, the multi-walled pipe has a double-walled construction in which the outer flow path portion (a sub pipe) through which the heated air flows is provided around the outer peripheral side of the inner flow path portion (a main pipe) through which the first fluid flows. Thus, it is possible to enhance the function of restraining the temperature decrease of the first fluid.

The waste heat output portion may be the condenser that cools and condenses the second fluid; and the second fluid may be air-cooled by a fan. In this case, the fan condenses the second fluid, and generates heated air with a flow velocity, and the heated air is supplied straight to the primary-side flow path.

The heat recovery system may further include a connection pipe that connects the waste heat output portion and the outer flow path portion of the multi-walled pipe, the connection pipe being configured to supply the heated air from the waste heat output portion; a first valve configured to allow and block an inflow of the heated air from the connection pipe to the outer flow path portion; a discharge pipe connected to the outer flow path portion to discharge the heated air; and a second valve configured to allow and block an outflow of the heated air from the outer flow path portion to the discharge pipe. In this case, when the second valve is closed to block the outflow of the heated air from the discharge pipe, the heated air resides in the outer flow path portion. This makes it possible to raise the temperature of the outer flow path portion for a predetermined time.

The multi-walled pipe may include a main pipe, a sub pipe, and an outer pipe; a heat insulating material may be provided at an outer periphery of the main pipe, and an inside of the main pipe may serve as the inner flow path portion; the sub pipe may be provided around an outer peripheral side of the main pipe such that a flow path with an annular cross section that serves as the outer flow path portion is configured; and the outer pipe may be provided around an outer peripheral side of the sub pipe such that a vacuum space with an annular cross section is configured. In this configuration, the multi-walled pipe has a triple-walled construction in which the outer flow path portion (the sub pipe) through which the heated air flows is provided around the outer peripheral side of the inner flow path portion (the main pipe) through which the first fluid flows, and further, the vacuum space is provided around the outer periphery of the outer flow path portion. Thus, it is possible to further enhance the function of restraining the temperature drop of the first fluid.

With the above aspect of the disclosure, it is possible to enhance the power generation efficiency by restraining the temperature drop of the first fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a plan view illustrating an example of a heat recovery system according to a first embodiment of the disclosure;

FIG. 2 illustrates oil tanks, a heat exchanger, and a power generation unit;

FIG. 3 illustrates the oil tanks, the heat exchanger, and the power generation unit;

FIG. 4 illustrates the oil tanks, the heat exchanger, and the power generation unit;

FIG. 5 is a graph indicating temporal variations in the temperature in each of chambers such as hardening chambers for heat treatment in a first furnace and a second furnace;

FIG. 6 indicates a relationship between the temperature of a cooling liquid in each of the first furnace and the second furnace and whether or not the power generation unit can generate electric power;

FIG. 7 indicates a relationship between the temperature of the cooling liquid in each of the first furnace and the second furnace and whether or not the power generation unit can generate electric power;

FIG. 8 illustrates a facility according to the related art in which a binary power generation unit is employed in conjunction with a heat treatment device for heat treatment of a metal part;

FIG. 9 indicates a relationship between the temperature of a cooling liquid and whether or not a power generation unit can generate electric power in the related art;

FIG. 10 is a schematic diagram illustrating an example of a heat recovery system according to a second embodiment of the disclosure;

FIG. 11 is a cross sectional view illustrating an example of a multi-walled pipe;

FIG. 12 is a longitudinal sectional view illustrating the example of the multi-walled pipe;

FIG. 13 is a cross sectional view illustrating a modification of the multi-walled pipe;

FIG. 14 illustrates a schematic configuration of a condenser, a connection pipe, a primary-side flow path, and surrounding components; and

FIG. 15 illustrates a facility according to the related art in which a binary power generation unit is employed in conjunction with a heat treatment device.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 is a plan view illustrating an example of a heat recovery system according to a first embodiment. In a heat recovery system 10, a power generation unit 14 generates electric power utilizing waste heat from heat treatment devices 12 that perform heat treatment on metal parts. Examples of the metal parts include mechanical parts such as a bearing ring of a rolling bearing, a shaft, and a pin. The heat treatment may be hardening treatment (quenching treatment). For the heat treatment (see FIG. 2), metal parts 7 (hereinafter referred to as “objects 7”) that have been heated are immersed in a cooling liquid (hardening oil, i.e., quenching oil) 18 in oil tanks 16 of the heat treatment devices 12 to be cooled. In this event, the temperature of the cooling liquid 18 is raised. Heat of the cooling liquid 18 is used for electric power generation. That is, the oil tanks 16 function as heat source portions, and the cooling liquid 18 serves as a heating medium (first fluid) on the primary side. Heat of the cooling liquid 18 is transmitted to a medium (second fluid) 19 on the secondary side by a heat exchanger 20, and the power generation unit 14 generates electric power. FIG. 2 illustrates the oil tanks 16, the heat exchanger 20, and the power generation unit 14. In the drawings, identical constituent elements are given identical symbols (reference numerals) to omit redundant description. In the present embodiment (see FIG. 2), a plurality of objects 7 are housed in a basket 8, and the basket 8 is moved up and down by an actuator (not illustrated).

The heat recovery system 10 illustrated in FIG. 1 includes two heat treatment devices 12. The heat treatment device 12 on the upper side in FIG. 1 will be referred to as a “first furnace 12 a”, and the heat treatment device 12 on the lower side will be referred to as a “second furnace 12 b”. The first furnace 12 a and the second furnace 12 b have the same configuration. The first furnace 12 a and the second furnace 12 b each include a first purge chamber 81, a first preheating chamber 82, a second preheating chamber 83, a carburization-diffusion chamber 84, a temperature drop chamber 85, a heat equalizing chamber 86, a hardening chamber (quenching chamber) 87, and a second purge chamber 88, which are arranged in this order from an upstream side (left side in FIG. 1) in the advancing direction of the objects 7. The hardening chambers 87 are provided with the respective oil tanks 16. Since the heat recovery system 10 includes two heat treatment devices 12, the heat recovery system 10 includes two oil tanks 16. The oil tank 16 of the first furnace 12 a will be referred to as a “first oil tank 16 a”. The oil tank 16 of the second furnace 12 b will be referred to as a “second oil tank 16 b”.

In FIG. 2, the heat recovery system 10 includes the heat exchanger 20, the power generation unit 14, and a valve mechanism 22, in addition to the oil tanks 16 (16 a and 16 b) that serve as heat source portions. The heat recovery system 10 further includes a primary flow path portion 24 and a secondary flow path portion 26. The primary flow path portion 24 connects the oil tanks 16 (16 a and 16 b) and the heat exchanger 20, and allows the cooling liquid 18 to pass therein (i.e., the cooling liquid 18 flows through the primary flow path portion 24). The secondary flow path portion 26 connects the heat exchanger 20 and the power generation unit 14, and allows the heating medium 19 on the secondary side to flow therein (i.e., the heating medium 19 on the secondary side flows through the secondary flow path portion 26). The heating medium 19 on the secondary side may be a liquid with a relatively low boiling point.

The oil tanks 16 store the cooling liquid 18. As described above, when the objects 7 that have been heated are immersed in the cooling liquid 18, the objects 7 are subjected to heat treatment (hardening treatment, i.e., quenching treatment). In this event, the temperature of the cooling liquid 18 is raised. That is, the temperature of the cooling liquid 18 is raised by heat obtained when the objects 7 are subjected to the heat treatment.

The heat exchanger 20 is connected to the two oil tanks 16 a and 16 b via the primary flow path portion 24 through which the cooling liquid 18 flows. In the heat exchanger 20, heat of the cooling liquid 18 is transmitted to the heating medium 19 on the secondary side. That is, the heat exchanger 20 performs heat exchange from the cooling liquid 18 to the heating medium 19 on the secondary side.

The primary flow path portion 24 includes a main flow path 28 and a coupling flow path 30. The main flow path 28 connects each of the oil tanks 16 a and 16 b to the heat exchanger 20. The coupling flow path 30 connects the oil tanks 16 a and 16 b to each other to enable movement of the cooling liquid 18 between the oil tanks 16 a and 16 b. The main flow path 28 includes a first pipe 31, a second pipe 32, and a third pipe 33. The first pipe 31 connects the first oil tank 16 a and the second oil tank 16 b. The first pipe 31 is provided with a first valve 34 and a second valve 35 that open and close. The second pipe 32, which is parallel to the first pipe 31, connects the first oil tank 16 a and the second oil tank 16 b. The second pipe 32 is provided with a third valve 36 and a fourth valve 37 that open and close. The third pipe 33 connects the first pipe 31 and the second pipe 32. The third pipe 33 is provided with a pump 39 that circulates the cooling liquid 18, and the heat exchanger 20. One end of the third pipe 33 is connected to a flow path of the first pipe 31 between the first valve 34 and the second valve 35. The other end of the third pipe 33 is connected to a flow path of the second pipe 32 between the third valve 36 and the fourth valve 37.

The coupling flow path 30 is formed by a pipe, and provided with a fifth valve 38 that opens and closes. Each of the valves 34, 35, 36, 37, and 38 operates to open and close on the basis of a command signal output from a control device (not illustrated). Control of the open/close operation may be executed by a control device that performs operation control (heat treatment control) for the first furnace 12 a and the second furnace 12 b. The secondary flow path portion 26 includes a fourth pipe 40 and a pump 41 that allows the heating medium 19 on the secondary side to be circulated between the heat exchanger 20 and the power generation unit 14.

The valve mechanism 22 is constituted by the first valve 34, the second valve 35, the third valve 36, the fourth valve 37, and the fifth valve 38. The valve mechanism 22 is provided in the primary flow path portion 24.

In the case where the fifth valve 38 is closed, the first valve 34 and the third valve 36 are open, and the second valve 35 and the fourth valve 37 are closed, the cooling liquid 18 in the first oil tank 16 a is returned to the first oil tank 16 a by way of a part of the second pipe 32, the third pipe 33, and a part of the first pipe 31. This flow is generated by the pump 39, and the cooling liquid 18 passes through the heat exchanger 20. This flow of the cooling liquid 18 will be referred to as a “first oil tank 16 a circulating flow”.

On the other hand, in the case where the fifth valve 38 is closed, the first valve 34 and the third valve 36 are closed, and the second valve 35 and the fourth valve 37 are open, the cooling liquid 18 in the second oil tank 16 b is returned to the second oil tank 16 b by way of a part of the second pipe 32, the third pipe 33, and a part of the first pipe 31. This flow is generated by the pump 39, and the cooling liquid 18 passes through the heat exchanger 20. This flow of the cooling liquid 18 will be referred to as a “second oil tank 16 b circulating flow”.

In this manner, the valve mechanism 22 functions to select a flow path that connects the heat exchanger 20 and the oil tanks 16 a and 16 b. In other words, the valve mechanism 22 selects one (16 a or 16 b) of the two oil tanks 16 a and 16 b to be connected to the heat exchanger 20. Specifically, the valve mechanism 22 has a first function of selecting one of the first oil tank 16 a circulating flow and the second oil tank 16 b circulating flow. The configuration of the primary flow path portion 24 to obtain the first oil tank 16 a circulating flow and the second oil tank 16 b circulating flow may be different from the illustrated configuration. Besides the first function described above, the valve mechanism 22 has the following second function.

In the case where the fifth valve 38 is open, the first valve 34 and the fourth valve 37 are open, and the second valve 35 and the third valve 36 are closed as illustrated in FIG. 3, the cooling liquid 18 in the first oil tank 16 a flows to the second oil tank 16 b through the coupling flow path 30, and is returned to the first oil tank 16 a by way of a part of the second pipe 32, the third pipe 33, and a part of the first pipe 31. This flow is generated by the pump 39, and the cooling liquid 18 passes through the heat exchanger 20. This flow of the cooling liquid 18 will be referred to as a “first system flow”.

On the other hand, in the case where the fifth valve 38 is open, the second valve 35 and the third valve 36 are open, and the first valve 34 and the fourth valve 37 are closed as illustrated in FIG. 4, the cooling liquid 18 in the second oil tank 16 b flows to the first oil tank 16 a through the coupling flow path 30, and is returned to the second oil tank 16 b by way of a part of the second pipe 32, the third pipe 33, and a part of the first pipe 31. This flow is generated by the pump 39, and the cooling liquid 18 passes through the heat exchanger 20. This flow of the cooling liquid 18 will be referred to as a “second system flow”.

In this manner, the valve mechanism 22 functions to select a flow path that connects the heat exchanger 20 and the oil tanks 16 a and 16 b. Specifically, the valve mechanism 22 has a second function of selecting one of the first system flow and the second system flow. The configuration of the primary flow path portion 24 to obtain the first system flow and the second system flow may be different from the illustrated configuration.

In FIGS. 2, 3, and 4, the power generation unit 14 is a binary power generation unit. The power generation unit 14 is connected to the heat exchanger 20 via the secondary flow path portion 26 through which the heating medium 19 on the secondary side flows. The power generation unit 14 generates electric power using the heating medium 19 as an input. The power generation unit 14 generates electric power in accordance with the temperature of the heating medium 19 on the secondary side. That is, the power generation unit 14 can generate electric power in the case where the heating medium 19 is at a predetermined temperature or higher, and cannot generate electric power in the case where the temperature of the heating medium 19 is lower than the predetermined temperature. That is, the power generation unit 14 can generate electric power in the case where the cooling liquid 18, which is used for heat exchange with the heating medium 19 is at a prescribed temperature or higher, and cannot generate electric power in the case where the temperature of the cooling liquid 18 is lower than the prescribed temperature.

First power generation operation will be described. That is, power generation operation performed by the heat recovery system 10 configured as described above will be described. FIG. 5 is a graph indicating temporal variations in the temperature (variations in the temperature with time) in each of chambers such as the hardening chambers 87 (see FIG. 1) for heat treatment in the first furnace 12 a and the second furnace 12 b. The upper part of FIG. 5 is a graph for the first furnace 12 a. The lower part of FIG. 5 is a graph for the second furnace 12 b. In each of the first furnace 12 a and the second furnace 12 b, the objects 7 are heated at a carburization temperature of about 950° C. in the carburization-diffusion chamber 84, and thereafter the objects 7 at a hardening temperature of about 850° C. are immersed in the cooling liquid 18 in the oil tank 16 to be quenched (hardened) in the hardening chamber 87. As indicated in FIG. 5, the time (timing) to start quenching of the objects 7 at the hardening temperature in the first furnace 12 a differs from the time (timing) to start quenching of the objects 7 at the hardening temperature in the second furnace 12 b. FIG. 5 indicates a case where the start of quenching in the second furnace 12 b is delayed from the start of quenching in the first furnace 12 a by a time Δt1. Heat treatment of the objects 7 is repeated in predetermined cycle times in each of the first furnace 12 a and the second furnace 12 b. The cycle time may be constant, or may be varied in accordance with the weight of the objects 7, for example.

FIG. 6 indicates a relationship between the temperature of the cooling liquid 18 in each of the first furnace 12 a and the second furnace 12 b and whether or not the power generation unit 14 can generate electric power. As indicated in FIG. 6, since the start of quenching in the second furnace 12 b is delayed from the start of quenching in the first furnace 12 a (time t0) by the time Δt1, the start of the temperature rise of the cooling liquid 18 in the second oil tank 16 b of the second furnace 12 b is delayed from the start of the temperature rise of the cooling liquid 18 in the first oil tank 16 a of the first furnace 12 a (from the start time t0) by the time Δt1. The time Δt1 will be referred to as a “delay time Δt1”.

When the temperature of the cooling liquid 18 in the first oil tank 16 a is raised to a prescribed temperature A or higher after the time t0, heat exchange is performed (i.e., heat is transferred) from the cooling liquid 18 to the heating medium 19 on the secondary side in the heat exchanger 20, which enables the power generation unit 14 to generate electric power. Therefore, in FIG. 2, the second valve 35, the fourth valve 37, and the fifth valve 38 are closed, and the first valve 34 and the third valve 36 are open. That is, the flow of the cooling liquid 18 is the “first oil tank 16 a circulating flow”. In this case, in FIG. 6, the temperature of the cooling liquid 18 in the first oil tank 16 a is raised to a certain value, and thereafter dropped. The power generation unit 14 can generate electric power for a continuation time Δt2 that lasts until the temperature becomes lower than the prescribed temperature A. In the present embodiment, the delay time Δt1 is set to be longer than the continuation time Δt2. The delay time Δt1 may be equal to the continuation time Δt2, or may be shorter than the continuation time Δt2.

In the case of FIG. 6, electric power cannot be generated for a time Δt3, which is the difference between the delay time Δt1 and the continuation time Δt2. When the temperature of the cooling liquid 18 in the second oil tank 16 b is raised to the prescribed temperature A or higher after the delay time Δt1 has elapsed since the start of the temperature rise of the cooling liquid 18 in the first oil tank 16 a (time t0), however, heat exchange is performed (i.e., heat is transferred) from the cooling liquid 18 to the heating medium 19 on the secondary side in the heat exchanger 20, which enables the power generation unit 14 to generate electric power. Therefore, valve opening-closing operation of the valve mechanism 22 is executed in FIG. 2, and the second valve 35 and the fourth valve 37 are opened (from the closed state), and the first valve 34 and the third valve 36 are closed (from the open state). The fifth valve 38 remains closed. That is, the flow of the cooling liquid 18 is switched to the “second oil tank 16 b circulating flow”.

In FIG. 6, the temperature of the cooling liquid 18 in the second oil tank 16 b is raised to a certain value, and thereafter dropped. The power generation unit 14 can generate electric power for a continuation time Δt4 that lasts until the temperature becomes lower than the prescribed temperature A. For a time Δt5 after the continuation time Δt4, the temperature of the cooling liquid 18 in the second oil tank 16 b is lower than the prescribed temperature A, and electric power cannot be generated. In the first furnace 12 a, however, other objects 7 are immersed in the first oil tank 16 a in the next cycle, that is, after the lapse of the cycle time T from the time t0, and the power generation unit 14 can generate electric power again through waste heat from the first furnace 12 a. Therefore, valve opening-closing operation of the valve mechanism 22 is executed in FIG. 2. The above operation is repeatedly executed thereafter.

In this manner, in the first power generation operation performed by the heat recovery system 10, operation control for the first furnace 12 a (first oil tank 16 a) and the second furnace 12 b (second oil tank 16 b) is performed such that the timing of the temperature rise of the cooling liquid 18 in the first oil tank 16 a, which serves as one heat source portion, is different from the timing of the temperature rise of the cooling liquid 18 in the second oil tank 16 b, which serves as the other heat source portion. The valve mechanism 22 operates in accordance with the timing of the temperature rise of the cooling liquid 18 in each of the two oil tanks 16 a and 16 b.

In the first power generation operation, the two oil tanks 16 a and 16 b share the power generation unit 14. Respective timings of the temperature rise of the cooling liquids 18 in the oil tank 16 a and in the oil tank 16 b are different from each other (in other words, the timing at which the temperature of the cooling liquid 18 in the first oil tank 16 a is raised is different from the timing at which the cooling liquid 18 in the second oil tank 16 b is raised). Therefore, when the cooling liquid 18, the temperature of which has been raised in the first oil tank 16 a, is supplied to the heat exchanger 20, heat exchange is performed (i.e., heat is transferred) from the cooling liquid 18 to the heating medium 19 on the secondary side, and the power generation unit 14 generates electric power using the heating medium 19 as an input. After that, even if the temperature of the first oil tank 16 a is dropped and electric power cannot be generated, the cooling liquid 18, the temperature of which has been raised in the second oil tank 16 b that is an oil tank other than the first oil tank 16 a, is supplied to the heat exchanger 20. Heat exchange is performed (i.e., heat is transferred) from the cooling liquid 18 to the heating medium 19 on the secondary side, and the power generation unit 14 can generate electric power using the heating medium 19 as an input. In this manner, the power generation unit 14 is given more opportunities to operate by making the timing of the temperature rise of the cooling liquid 18 in the oil tank 16 a different from the timing of the temperature rise of the cooling liquid 18 in the oil tank 16 b. Specifically (see FIG. 6), the cycle time T is set to 30 minutes, and the continuation time Δt2 (Δt4) for which the power generation unit 14 can generate electric power is set to 10 minutes. In the example according to the related art indicated in FIG. 9, electric power can be generated for one-third (10 minutes) of each cycle time T, and electric power cannot be generated for the remaining two-thirds (20 minutes). In the first power generation operation indicated in FIG. 6, in contrast, electric power can be generated for two-thirds (20 minutes) of each cycle time T, and electric power cannot be generated for the remaining one-third (10 minutes). Thus, electric power generation by the power generation unit 14 can be performed efficiently.

Second power generation operation will be described. The heat recovery system 10 configured as described above can perform power generation operation that is different from the first power generation operation. The second power generation operation will be described below. As described above (see FIG. 3), the primary flow path portion 24 includes the main flow path 28 that connects each of the first oil tank 16 a and the second oil tank 16 b to the heat exchanger 20, and the coupling flow path 30 that connects the first oil tank 16 a and the second oil tank 16 b to each other to enable movement of the cooling liquid 18 between the first oil tank 16 a and the second oil tank 16 b.

When the objects 7 that have been heated are immersed in the cooling liquid 18 in the first oil tank 16 a as illustrated in FIG. 3, opening-closing of the valves 34 to 38 is controlled in order that the flow of the cooling liquid 18 should become the “first system flow” with the use of the valve mechanism 22. Thus, the temperature of the cooling liquid 18 in the first oil tank 16 a is first raised. In this case, the cooling liquid 18 in the first oil tank 16 a flows to the second oil tank 16 b through the coupling flow path 30, and the cooling liquid 18 flows to the heat exchanger 20 by way of the second oil tank 16 b. Then, in the heat exchanger 20, heat exchange (i.e., heat transfer) to the heating medium 19 on the secondary side is performed. This enables the power generation unit 14 to generate electric power.

On the other hand, when the objects 7 that have been heated are immersed in the cooling liquid 18 in the second oil tank 16 b as illustrated in FIG. 4, opening-closing of the valves 34 to 38 is controlled in order that the flow of the cooling liquid 18 should become the “second system flow” with the use of the valve mechanism 22. Thus, the temperature of the cooling liquid 18 in the second oil tank 16 b is first raised. In this case, the cooling liquid 18 in the second oil tank 16 b flows to the first oil tank 16 a through the coupling flow path 30, and the cooling liquid 18 flows to the heat exchanger 20 by way of the first oil tank 16 a. Then, in the heat exchanger 20, heat exchange (i.e., heat transfer) to the heating medium 19 on the secondary side is performed. This enables the power generation unit 14 to generate electric power.

In this manner, in the second power generation operation illustrated in FIGS. 3 and 4, since the first oil tank 16 a and the second oil tank 16 b are connected to each other through the coupling flow path 30, the first oil tank 16 a and the second oil tank 16 b can be regarded as a single oil tank, and the volume of the cooling liquid 18 that serves as a heat source is increased. Therefore, the temperature rise of the cooling liquid 18 due to heat obtained through heat treatment of the objects 7 is mitigated as compared to the case (see FIG. 6) of the first power generation operation, but the temperature of the cooling liquid 18 that has been raised is not easily lowered. That is, the time (Δt2 and Δt4 in FIG. 6) for which the temperature of the cooling liquid 18 is the prescribed temperature A or higher is elongated. Thus, it is possible to elongate the time (i.e., time period) for which the power generation unit 14 can generate electric power as compared to the related art.

Third power generation operation will be described. The heat recovery system 10 configured as described above can perform power generation operation that is different from the first power generation operation and the second power generation operation. The third power generation operation will be described below. In the third power generation operation, as in the case of the first power generation operation, the timing of the temperature rise of the cooling liquid 18 in the first oil tank 16 a and the timing of the temperature rise of the cooling liquid 18 in the second oil tank 16 b are different from each other. In addition, as in the case of the second power generation operation, the flow path in the primary flow path portion 24 is switched by the valve mechanism 22 such that the cooling liquid 18 in the first oil tank 16 a flows to the second oil tank 16 b through the coupling flow path 30 and the cooling liquid 18 flows to the heat exchanger 20 by way of the second oil tank 16 b at the timing when the temperature of the cooling liquid 18 in the first oil tank 16 a is raised. On the other hand, the flow path in the primary flow path portion 24 is switched by the valve mechanism 22 such that the cooling liquid 18 in the second oil tank 16 b flows to the first oil tank 16 a through the coupling flow path 30 and the cooling liquid 18 flows to the heat exchanger 20 by way of the first oil tank 16 a at the timing when the temperature of the cooling liquid 18 in the second oil tank 16 b is raised.

As in the second power generation operation, since the first oil tank 16 a and the second oil tank 16 b are connected to each other through the coupling flow path 30, the oil tanks 16 a and 16 b can be regarded as a single oil tank, and the volume of the cooling liquid 18 that serves as a heat source is increased. Therefore, as indicated in FIG. 7, the temperature rise of the cooling liquid 18 due to heat obtained by treating the objects 7 is mitigated, but the temperature of the cooling liquid 18 that has been raised is not easily lowered. Thus, it is possible to elongate the time (continuation times Δt2 and Δt4) for which the power generation unit 14 can generate electric power. Further, as in the first power generation operation, the power generation unit 14 is given more opportunities to operate by making the timing of the temperature rise of the cooling liquid 18 in the oil tank 16 a different from the timing of the temperature rise of the cooling liquid 18 in the oil tank 16 b. FIG. 7 indicates a relationship between the temperature of the cooling liquid 18 in each of the first furnace 12 a and the second furnace 12 b and whether or not the power generation unit 14 can generate electric power in the case of the third power generation operation.

In the third power generation operation, the continuation time Δt2, for which electric power can be generated through waste heat from the first furnace 12 a, is elongated. Therefore, the time Δt3, for which electric power cannot be generated, is shortened (eliminated) as compared to the case of the first power generation operation indicated in FIG. 6. The flow path in the primary flow path portion 24 is switched by the valve mechanism 22 such that electric power can be generated through waste heat from the second furnace 12 b before it becomes impossible to generate electric power using waste heat from the first furnace 12 a. That is, the flow of the cooling liquid 18 is changed from the “first system flow” to the “second system flow” before (or when) it becomes impossible to generate electric power using waste heat from the first furnace 12 a. Then, electric power can be generated using waste heat from the second furnace 12 b subsequently to the continuation time Δt2 in FIG. 7. Moreover, the continuation time Δt4, for which electric power can be generated using waste heat from the second furnace 12 b, is elongated. Therefore, the time Δt5, for which electric power cannot be generated, is shortened (eliminated) as compared to the case of the first power generation operation indicated in FIG. 6. The flow path in the primary flow path portion 24 is switched by the valve mechanism 22 such that electric power can be generated using waste heat from the first furnace 12 a before (or when) it becomes impossible to generate electric power using waste heat from the second furnace 12 b. That is, the flow of the cooling liquid 18 is changed from the “second system flow” to the “first system flow” before (or when) it becomes impossible to generate electric power using waste heat from the second furnace 12 b.

In the third power generation operation indicated in FIG. 7, electric power can be generated through all the cycle times T. Thus, electric power generation by the power generation unit 14 can be performed efficiently.

The heat recovery system 10 according to the present embodiment will be described. In the heat treatment device 12 that performs heat treatment of the objects 7 in FIG. 1, the state for heat treatment (i.e., the state with regard to heat treatment) may be varied from moment to moment. Therefore, the temperature of waste heat obtained from the oil tanks 16 a and 16 b is unsteady. With the second power generation operation and the third power generation operation performed by the heat recovery system 10 according to the present embodiment, however, the waste heat can be leveled (equalized) as much as possible, and the waste heat can be efficiently utilized for heat generation.

Regarding the first power generation operation (see FIG. 6) performed by the heat recovery system 10 according to the present embodiment, the start of the temperature rise of the cooling liquid 18 in the second oil tank 16 b is delayed from the start of the temperature rise of the cooling liquid 18 in the first oil tank 16 a (time t0) by the time Δt1, which is defined as the “delay time Δt1”. As described above, the temperature of waste heat obtained from the oil tanks 16 a and 16 b is unsteady. Thus, the delay time Δt1 may be changed in accordance with the temperature of the waste heat (temperature of the cooling liquid 18), instead of being constant. That is, the timing when the flow of the cooling liquid 18 is switched by the valve mechanism 22 between the “first oil tank 16 a circulating flow” and the “second oil tank 16 b circulating flow” may be varied in accordance with the temperature of the cooling liquid 18 in the first oil tank 16 a and the second oil tank 16 b.

In the embodiment described above, the two heat treatment devices 12 share one power generation unit 14. However, three or more heat treatment devices 12 may be provided instead of providing two heat treatment devices 12, as long as a plurality of heat treatment devices 12 are provided.

The heat treatment devices 12 are not limited to continuous carburizing hardening (quenching) furnaces such as those illustrated in FIG. 1, and may be batch carburizing hardening furnaces, for example. The combination of the plurality of heat treatment devices 12 may be a combination of a continuous carburizing hardening furnace and a batch carburizing hardening furnace. While the carburizing hardening furnaces are described above as examples, the disclosure is not limited thereto. The cooling liquid may be oil, water, a polymer, etc. A cooling gas may be used in place of the cooling liquid. The object facilities are not limited to the carburizing hardening furnaces, and may be heat treatment furnaces that have hardening tanks, such as hardening furnaces (quenching furnaces), carbonitriding hardening furnaces, vacuum carburizing hardening furnaces, and vacuum hardening furnaces. In the embodiment in FIG. 1, waste heat from the oil tanks 16 of the hardening chambers 87 is used for electric power generation. However, heat from an exhaust gas from a regenerative burner in the preheating chambers 82 (83) or heat from a cooling tube in the temperature drop chambers 85 may be used as a heat source. In this case, the preheating chambers 82 (83) (or the temperature drop chambers 85) serve as heat source portions, and a part of the preheating chamber 82 (83) (or the temperature drop chamber 85) of the first furnace 12 a and a part of the preheating chamber 82 (83) (or the temperature drop chamber 85) of the second furnace 12 b are connected to each other through the coupling flow path 30 etc.

In the embodiment described above, the power generation unit 14 is combined with the heat treatment devices 12. However, the power generation unit 14 may be combined with facilities other than the heat treatment devices 12. In the case where electric power is generated through waste heat obtained from a factory or facilities such as the heat treatment devices 12, the waste heat may be in a high temperature range or a low temperature range. With the configuration of the embodiment described above, however, the waste heat can be recovered stably to enable efficient electric power generation.

The embodiment disclosed above is exemplary in all respects, and not limiting. The scope of the disclosure is not limited to the embodiment discussed above, and includes all modifications that fall within the scope of the disclosure.

FIG. 10 is a schematic diagram illustrating an example of a heat recovery system according to a second embodiment. An overview of a heat recovery system 10 according to the present embodiment will be described. In the heat recovery system 10, a power generation unit (binary power generation unit) 14 generates electric power utilizing waste heat from a heat treatment device 12 that performs heat treatment of metal parts. Examples of the metal parts include mechanical parts such as a bearing ring of a rolling bearing, a shaft, and a pin. The heat treatment may be hardening treatment (i.e., quenching treatment). For the heat treatment, metal parts 7 (hereinafter referred to as “objects 7”) that have been heated are immersed in a cooling liquid (hardening oil, i.e., quenching oil) 18 in an oil tank 16 of the heat treatment device 12 to be cooled. In the present embodiment, a plurality of objects 7 are housed in a basket 8, and the basket 8 is moved up and down by an actuator 9. When the basket 8 is lowered, the objects 7 are immersed in the cooling liquid 18 to be cooled.

The temperature of the cooling liquid 18 is raised when the objects 7 that have been heated are immersed in the cooling liquid 18. Heat of the cooling liquid 18 is used for electric power generation by the power generation unit 14. That is, the oil tank 16 functions as a heat source, and the cooling liquid 18 serves as a heating medium (first fluid) on the primary side. Heat of the cooling liquid 18 is transmitted to a heating medium (second fluid) 19 on the secondary side by the heat exchanger 20 of the power generation unit 14, and a power generation device 122 generates electric power.

A specific configuration of the heat recovery system 10 will be described. The heat recovery system 10 illustrated in FIG. 10 is provided by applying the power generation unit (binary power generation unit) 14 to the heat treatment device 12 that performs heat treatment (hardening treatment, i.e., quenching treatment) of the objects 7.

The heat treatment device 12 includes a first purge chamber 81, a first preheating chamber 82, a second preheating chamber 83, a carburization-diffusion chamber 84, a temperature drop chamber 85, a heat equalizing chamber 86, a hardening chamber (quenching chamber) 87, and a second purge chamber 88, which are arranged in this order from the upstream side (left side in FIG. 10) in the advancing direction of the objects 7. The hardening chamber 87 is provided with the oil tank 16.

The power generation unit 14 includes a primary-side flow path 131, the heat exchanger (vaporizer) 20, a secondary-side flow path 132, the power generation device 122, and a condenser 124.

The cooling liquid 18 flows to the primary-side flow path 131 from an oil tank 16 that serves as a heat source. Specifically, the primary-side flow path 131 includes a first pipe 140 and a second pipe 142. The first pipe 140 connects the oil tank 16 that serves as a heat source and the heat exchanger 20. The cooling liquid 18 flows through the first pipe 140 from the oil tank 16 to the heat exchanger 20. The second pipe 142 connects the heat exchanger 20 and the oil tank 16. The cooling liquid 18 flows through the second pipe 142 from the heat exchanger 20 to the oil tank 16. As described later, the first pipe 140 includes a multi-walled pipe 50 that includes a plurality of independent flow paths that extend in the longitudinal direction. The multi-walled pipe 50 may be a part of the first pipe 140. In the present embodiment, however, all of the first pipe 140 is formed by the multi-walled pipe 50. In this way, the primary-side flow path 131 includes the multi-walled pipe 50.

The heat exchanger 20 performs heat exchange (i.e., transfers heat) from the cooling liquid 18 that flows through the primary-side flow path 131 (the first pipe 140) to the heating medium 19 on the secondary side. The temperature of the cooling liquid 18 that flows through the first pipe 140 is about 120 to 130° C., for example. The heating medium 19 on the secondary side has a relatively low boiling point. Various fluids can be adopted for the heating medium 19 on the secondary side. Examples of such fluids include a chlorofluorocarbon substitute (HFC245fa). In the heat exchanger 20, heat of the cooling liquid 18 is transmitted to the heating medium 19 on the secondary side to gasify the heating medium 19. When the heating medium 19 deprives the cooling liquid 18 of heat, the cooling liquid 18 is cooled, and returned to the oil tank 16.

The heating medium 19 that has been gasified in the heat exchanger 20 flows through the secondary-side flow path 132. The secondary-side flow path 132 is formed by a looped pipe. The heat exchanger 20, the power generation device 122, the condenser 124, etc. are provided at various positions in the secondary-side flow path 132.

The power generation device 122 includes an expansion unit (scroll expansion unit) 126. Electric power is generated using the heating medium 19 on the secondary side that is input from the heat exchanger 20 to the expansion unit 126. The heating medium 19 that has passed through the power generation device 122 (expansion unit 126) is input to the condenser 124. The heating medium 19 that has passed through the power generation device 122 is hotter than the normal temperature (i.e., the ordinary temperature) by about 30 to 40° C., for example, and is still in a gaseous state. The heating medium 19 is liquefied when the heating medium 19 is cooled in the condenser 124. The heating medium 19 that has been liquefied flows to the heat exchanger 20, and heat exchange is performed between the heating medium 19 and the cooling liquid 18.

As described above, the heating medium 19 on the secondary side is cooled and liquefied in the condenser 124. The heating medium 19 is cooled to about the normal temperature, for example. The condenser 124 according to the present embodiment air-cools the heating medium 19 using a fan (in other words, in the condenser 124, the heating medium 19 is air-cooled by a fan). One end 45 of a connection pipe 44 is connected to the condenser 124. Heat of the heating medium 19 is transmitted to ambient air in the condenser 124. The ambient air becomes heated air (hot air), and is taken into the connection pipe 44 to flow toward the other end 46 of the connection pipe 44. The temperature of the heated air that is obtained using heat output from the condenser 124 is higher than the ambient temperature (outside air: normal temperature) around the primary-side flow path 131. The other end 46 of the connection pipe 44 is connected to an outer flow path portion 136 (see FIGS. 11 and 12) (to be discussed later) of the multi-walled pipe 50 of the primary-side flow path 131.

The multi-walled pipe 50 will be described. FIG. 11 is a cross sectional view illustrating an example (overview) of the multi-walled pipe 50. FIG. 12 is a longitudinal sectional view illustrating an example (overview) of the multi-walled pipe 50. The multi-walled pipe 50 includes a main pipe 52 having an outer periphery at which a heat insulating material 54 is provided, and a sub pipe 56 provided around an outer peripheral side of the main pipe 52. Each of the main pipe 52 and the sub pipe 56 is formed by a pipe made of metal, for example. The heat insulating material 54 covers the entire periphery (i.e., entire circumference) of the main pipe 52. A flow path with an annular cross section is provided between an outer peripheral surface of the heat insulating material 54 and the sub pipe 56. In the present embodiment, a second heat insulating material 58 is provided at an outer periphery of the sub pipe 56. The heat insulating materials 54 and 58 are made of glass wool, for example.

The inside of the main pipe 52 serves as an inner flow path portion 134 through which the cooling liquid 18 flows. As illustrated in FIG. 12, the connection pipe 44 that is provided to extend from the condenser 124 is connected to the outer flow path portion 136. The flow path with the annular cross section on an inner peripheral side of the sub pipe 56 serves as the outer flow path portion 136. The heated air that has passed through the connection pipe 44 flows through the outer flow path portion 136. A discharge pipe 48 is connected to the multi-walled pipe 50. The discharge pipe 48 is connected to the outer flow path portion 136, and the heated air is discharged from the discharge pipe 48.

A first valve 61 is provided at the other end 46 of the connection pipe 44. An inflow of the heated air from the connection pipe 44 to the outer flow path portion 136 is allowed when the first valve 61 is open, and the inflow of the heated air from the connection pipe 44 to the outer flow path portion 136 is blocked when the first valve 61 is closed. A second valve 62 is provided in the discharge pipe 48. An outflow of the heated air from the outer flow path portion 136 to the outside is allowed when the second valve 62 is open, and the outflow of the heated air from the outer flow path portion 136 to the outside is blocked when the second valve 62 is closed.

As described above, the multi-walled pipe 50 includes the inner flow path portion 134 through which the cooling liquid 18 passes, and the outer flow path portion 136 that is provided around the inner flow path portion 134. The heated air that is obtained using heat output from the condenser 124 and that has flowed through the connection pipe 44 passes through the outer flow path portion 136.

FIG. 13 is a cross sectional view illustrating a modification of the multi-walled pipe 50. The multi-walled pipe 50 illustrated in FIG. 13 includes a main pipe 52 having an outer periphery at which a heat insulating material 54 is provided, a sub pipe 56 provided around the outer peripheral side of the main pipe 52, and an outer pipe 60 provided around the outer peripheral side of the sub pipe 56. As in the form illustrated in FIG. 11, the inside of the main pipe 52 serves as the inner flow path portion 134. The sub pipe 56 is provided away from the heat insulating material 54 in the radial direction to form a flow path with an annular cross section that serves as the outer flow path portion 136 (in other words, the sub pipe 56 is provided away from the heat insulating material 54 in the radial direction such that a flow path with an annular cross section that serves as the outer flow path portion 136 is provided). A second heat insulating material 58 is provided at the outer periphery of the sub pipe 56. The outer pipe 60 is provided away from the second heat insulating material 58 in the radial direction, and a sealed space with an annular cross section is formed between the outer pipe 60 and the heat insulating material 58. This sealed space serves as a vacuum space 59.

FIG. 14 illustrates a schematic configuration of the condenser 124, the connection pipe 44, the primary-side flow path 131, and surrounding components. In the present embodiment, as described above, the first pipe 140 of the primary-side flow path 131 includes a multi-walled pipe 50. The condenser 124 and the outer flow path portion 136 (see FIGS. 11 and 12) of the multi-walled pipe 50 are connected to each other through the connection pipe 44. The heated air that is supplied from the condenser 124 flows through the connection pipe 44 to be supplied to the outer flow path portion 136.

The connection pipe 44 illustrated in FIG. 14 includes a main connection pipe 64 connected to the condenser 124, and branch pipes 65 and 66 branched from the main connection pipe 64. The branch pipe 65 is connected to a downstream side (a heat exchanger 20 side) of the multi-walled pipe 50. The branch pipe 66 is connected to the upstream side (an oil tank 16 side) of the multi-walled pipe 50. The discharge pipe 48 is connected to an intermediate portion in the middle area of the multi-walled pipe 50. In the case of this configuration, the heated air that has flowed from the condenser 124 through the main connection pipe 64 passes through each of the branch pipes 65 and 66 to flow into the outer flow path portion 136 of the multi-walled pipe 50. The heated air that has flowed into the outer flow path portion 136 flows along the longitudinal direction of the multi-walled pipe 50, and is discharged from the discharge pipe 48.

The connection pipe 44 may be configured differently from that illustrated in FIG. 14. For example, the connection pipe 44 may be directly connected to the upstream side (the oil tank 16 side) of the multi-walled pipe 50 without being branched as illustrated in FIG. 14. In this case, the discharge pipe 48 is connected to the downstream side (the heat exchanger 20 side) of the multi-walled pipe 50. Alternatively, the connection pipe 44 may be directly connected to the downstream side (the heat exchanger 20 side) of the multi-walled pipe 50 without being branched. In this case, the discharge pipe 48 is connected to the upstream side (the oil tank 16 side) of the multi-walled pipe 50.

As described above, the heat recovery system 10 (see FIG. 10) according to the present embodiment includes the primary-side flow path 131 through which the cooling liquid 18 flows from the oil tank 16 that serves as a heat source, the heat exchanger 20, the secondary-side flow path 132 through which the heating medium 19 on the secondary side flows, the power generation device 122, and the condenser 124. The heat exchanger 20 performs heat exchange (i.e., transfers heat) from the cooling liquid 18 that flows through the primary-side flow path 131 to the heating medium 19 on the secondary side. The power generation device 122 generates electric power using the heating medium 19 in the secondary-side flow path 132. The heating medium 19 that has passed through the power generation device 122 (expansion unit 126) is input to the condenser 124 such that heat exchange is performed between the heating medium 19 and the ambient air. The primary-side flow path 131 includes the multi-walled pipe 50. As illustrated in FIGS. 11 and 12 (FIG. 13), the multi-walled pipe 50 includes the inner flow path portion 134 through which the cooling liquid 18 passes, and the outer flow path portion 136 that is provided around the inner flow path portion 134. The heated air that is obtained using heat output from the condenser 124 passes through the outer flow path portion 136.

With the heat recovery system 10, the energy that has been discarded as waste heat in the related art, that is, thermal energy that is output from the condenser 124, can be utilized again. That is, the temperature drop due to heat release from the cooling liquid 18 that flows through the inner flow path portion 134 of the multi-walled pipe 50 can be restrained by supplying the heated air that is obtained using heat output from the condenser 124 to the outer flow path portion 136 of the multi-walled pipe 50. Heat exchange can be performed (i.e., heat can be transferred) with a high thermal efficiency from the cooling liquid 18 to the heating medium 19 on the secondary side. As a result, it is possible to enhance the efficiency of electric power generation (binary electric power generation) in which the heating medium 19 is used.

In the present embodiment, as illustrated in FIG. 14, the primary-side flow path 131 includes the first pipe 140 that allows the cooling liquid 18 to flow from the oil tank 16 to the heat exchanger 20, and the second pipe 142 that allows the cooling liquid 18 to flow from the heat exchanger 20 to the oil tank 16. The first pipe 140 includes the multi-walled pipe 50. The condenser 124 and the outer flow path portion 136 of the multi-walled pipe 50 are connected to each other through the connection pipe 44. The effect of retaining heat of the cooling liquid 18 that flows through the inner flow path portion 134 can be enhanced by the heated air that is supplied to the outer flow path portion 136 through the connection pipe 44. Therefore, the temperature drop of the cooling liquid 18 that flows to the heat exchanger 20 through the first pipe 140 can be restrained effectively.

As illustrated in FIGS. 11 and 12, the multi-walled pipe 50 according to the present embodiment includes the main pipe 52 having the outer periphery at which the heat insulating material 54 is provided, and the sub pipe 56 which is provided around the outer peripheral side of the main pipe 52 and in which a flow path with an annular section is formed to serve as the outer flow path portion 136. That is, the multi-walled pipe 50 has a double-walled construction (double-pipe structure) in which the outer flow path portion 136 (the sub pipe 56) through which the heated air flows is provided around the outer peripheral side of the inner flow path portion 134 (the main pipe 52) through which the cooling liquid 18 flows.

In the modification, as illustrated in FIG. 13, the multi-walled pipe 50 may have a triple-walled construction (triple-pipe structure). That is, the multi-walled pipe 50 includes the main pipe 52, the sub pipe 56, and the outer pipe 60 that are arranged in this order from the center. The heat insulating material 54 is provided at the outer periphery of the main pipe 52. The inside of the main pipe 52 serves as the inner flow path portion 134. The sub pipe 56 is provided around the outer peripheral side of the main pipe 52, and a flow path with an annular section that serves as the outer flow path portion 136 is formed between the main pipe 52 and the sub pipe 56. The outer pipe 60 is provided around the outer peripheral side of the sub pipe 56, and forms the vacuum space 59 with an annular section. In this modification, the outer flow path portion 136 (the sub pipe 56) through which the heated air flows is provided around the outer peripheral side of the inner flow path portion 134 (the main pipe 52) through which the cooling liquid 18 flows and, further, the vacuum space 59 is provided at the outer periphery of the outer flow path portion 136. Therefore, it is possible to further enhance the function of restraining the temperature drop of the cooling liquid 18.

As illustrated in FIG. 14, the condenser 124 cools and condenses the heating medium 19 on the secondary side. In the present embodiment, the condenser 124 air-cools the heating medium 19 using a fan. Therefore, the fan condenses the heating medium 19, and generates heated air with a flow velocity. Therefore, this heated air is supplied immediately to the primary-side flow path 131 (the multi-walled pipe 50 of the first pipe 140) through the connection pipe 44.

As illustrated in FIG. 14, the heat recovery system 10 according to the present embodiment further includes the connection pipe 44, the first valve 61, the discharge pipe 48, and the second valve 62. The connection pipe 44 connects the condenser 124 and the outer flow path portion 136 of the multi-walled pipe 50, and heated air from the condenser 124 flows through the connection pipe 44. The first valve 61 has a function of allowing and blocking an inflow of heated air from the connection pipe 44 to the outer flow path portion 136 through opening-closing operation. The discharge pipe 48 is connected to the outer flow path portion 136 to discharge heated air. The second valve 62 has a function of allowing and blocking an outflow of heated air from the outer flow path portion 136 to the discharge pipe 48 through opening-closing operation. With this configuration, when the second valve 62 is closed to block a flow of heated air out of the discharge pipe 48, the heated air resides in the outer flow path portion 136. Consequently, it is possible to raise the temperature of the outer flow path portion 136 for a predetermined time. The first valve 61 may also be closed when the second valve 62 is closed. When the predetermined time elapses, the temperature of the outer flow path portion 136 starts dropping. Thus, the second valve 62 (and the first valve 61) is opened to introduce new heated air to the outer flow path portion 136. Such opening-closing operation of the valves 61 and 62 may be performed repeatedly.

In the embodiment described above, the ambient air is heated using waste heat obtained from the condenser 124 of the power generation unit 14, and thus, heated air is obtained. That is, the condenser 124 is the generation source of the heated air. The generation source of the heated air may be other than the condenser 124 described above. That is, the heated air may be obtained from waste heat generated by a different constituent element. A waste heat output portion (generation source) that outputs waste heat to generate heated air may be the oil tank 16 of the heat treatment device 12 (see FIG. 10), or may be the carburization-diffusion chamber 84 that generates a hot gas, in addition to or instead of the condenser 124. The waste heat output portion may also be a constituent element (oil tank or carburization-diffusion chamber) of another heat treatment device provided, for example, in the vicinity of the heat treatment device 12 to which the power generation unit 14 is applied. In this manner, the waste heat output portion that outputs heat for obtaining heated air may be at least one of the heat source (oil tank 16), another heat source, and the condenser 124.

The embodiments disclosed above are exemplary in all respects, and not limiting. The scope of the disclosure is not limited to the embodiments discussed above, and includes all modifications that fall within the scope of the disclosure.

The form of the heat treatment device 12 may be different from the form illustrated in FIG. 10, and may be a batch treatment furnace, instead of a continuous treatment furnace. The heat source for performing binary electric power generation may be other than the oil tank 16. The device that includes the heat source may be other than the heat treatment device 12. For example, the heat recovery system 10 may be employed for an apparatus for geothermal electric power generation. 

What is claimed is:
 1. A heat recovery system comprising: a plurality of heat source portions configured to raise a temperature of a first fluid using heat obtained by treating an object; a heat exchanger connected to the plurality of heat source portions via a primary flow path portion through which the first fluid flows, and configured to perform heat exchange between the first fluid and a second fluid; a valve mechanism provided in the primary flow path portion and configured to select a flow path that connects the heat exchanger and the heat source portions; and a power generation unit connected to the heat exchanger via a secondary flow path portion through which the second fluid flows, and configured to generate electric power using the second fluid as an input, wherein timing of a temperature rise of the first fluid in one of the heat source portions is different from timing of a temperature rise of the first fluid in another of the heat source portions, and the valve mechanism operates in accordance with the timing of the temperature rise of the first fluid in each of the plurality of heat source portions.
 2. The heat recovery system according to claim 1, wherein: the primary flow path portion includes a main flow path that connects the heat source portions and the heat exchanger, and a coupling flow path that connects the heat source portions to each other to enable movement of the first fluid between the heat source portions; and the valve mechanism includes a valve configured to switch the flow path such that, in a case where the temperature of the first fluid in the one heat source portion is raised, the first fluid flows to the other heat source portion through the coupling flow path and the first fluid flows to the heat exchanger by way of the other heat source portion.
 3. The heat recovery system according to claim 1, wherein the power generation unit is a binary power generation unit.
 4. A heat recovery system comprising: a plurality of heat source portions configured to raise a temperature of a first fluid using heat obtained by treating an object; a heat exchanger connected to the plurality of heat source portions via a primary flow path portion through which the first fluid flows, and configured to perform heat exchange between the first fluid and a second fluid; a valve mechanism provided in the primary flow path portion and configured to select a flow path that connects the heat exchanger and the heat source portions; and a power generation unit connected to the heat exchanger via a secondary flow path portion through which the second fluid flows, and configured to generate electric power using the second fluid as an input, wherein: the primary flow path portion includes a main flow path that connects the heat source portions and the heat exchanger, and a coupling flow path that connects the heat source portions to each other to enable movement of the first fluid between the heat source portions; and the valve mechanism includes a valve configured to switch the flow path such that, in a case where the temperature of the first fluid in one of the heat source portions is raised, the first fluid flows to another of the heat source portions through the coupling flow path and the first fluid flows to the heat exchanger by way of the other heat source portion.
 5. The heat recovery system according to claim 4, wherein the power generation unit is a binary power generation unit.
 6. A heat recovery system comprising: a primary-side flow path through which a first fluid flows from a heat source; a heat exchanger configured to perform heat exchange between the first fluid, which flows through the primary-side flow path, and a second fluid; a secondary-side flow path through which the second fluid flows; a power generation device configured to generate electric power using the second fluid in the secondary-side flow path; and a condenser configured to cool and condense the second fluid that has passed through the power generation device, wherein: the primary-side flow path includes a multi-walled pipe that includes an inner flow path portion through which the first fluid passes and an outer flow path portion provided around the inner flow path portion; and the outer flow path portion is supplied with heated air obtained through heat output from a waste heat output portion that is at least one of the heat source, another heat source, and the condenser.
 7. The heat recovery system according to claim 6, wherein: the primary-side flow path includes a first pipe that allows the first fluid to flow from the heat source to the heat exchanger; the first pipe includes the multi-walled pipe; and the heat recovery system includes a connection pipe through which the heated air is supplied from the waste heat output portion to the outer flow path portion of the multi-walled pipe.
 8. The heat recovery system according to claim 6, wherein: the multi-walled pipe includes a main pipe and a sub pipe; a heat insulating material is provided at an outer periphery of the main pipe, and an inside of the main pipe serves as the inner flow path portion; and the sub pipe is provided around an outer peripheral side of the main pipe such that a flow path with an annular cross section that serves as the outer flow path portion is configured.
 9. The heat recovery system according to claim 6, wherein: the waste heat output portion is the condenser that cools and condenses the second fluid; and the second fluid is air-cooled by a fan.
 10. The heat recovery system according to claim 6, further comprising: a connection pipe that connects the waste heat output portion and the outer flow path portion of the multi-walled pipe, the connection pipe being configured to supply the heated air from the waste heat output portion; a first valve configured to allow and block an inflow of the heated air from the connection pipe to the outer flow path portion; a discharge pipe connected to the outer flow path portion to discharge the heated air; and a second valve configured to allow and block an outflow of the heated air from the outer flow path portion to the discharge pipe.
 11. The heat recovery system according to claim 6, wherein: the multi-walled pipe includes a main pipe, a sub pipe, and an outer pipe; a heat insulating material is provided at an outer periphery of the main pipe, and an inside of the main pipe serves as the inner flow path portion; the sub pipe is provided around an outer peripheral side of the main pipe such that a flow path with an annular cross section that serves as the outer flow path portion is provided; and the outer pipe is provided around an outer peripheral side of the sub pipe such that a vacuum space with an annular cross section is configured. 